The preparation of organic acids by oxidation of compounds such as alcohols, esters, ethers, ketones or aldehydes with nitric acid often is characterized by violent or even explosively runaway reactions which have required extremely careful control of reaction conditions by cooling and/or stepwise addition of reactants. For example, the oxidation of aldoses, other monosaccharides, disaccharides, oligosaccharides or polysaccharides to aldonic or aldaric acids using nitric acid as the oxidizing agent according to typical procedures (J. Stanek, M. Cerny, J. Kocourek and J. Pacak, "The Monosaccharides", Academic Press, New York, 1963, p 744 and references 3-41 therein) is characterized by an exothermic step or steps in the early part of the oxidation (W. N. Haworth and W. G. M. Jones, J. Chem. Soc., 1944, 65-7) that results in a rapid temperature rise (generally to 90.degree. C. or higher) that is difficult to control by cooling. The threat of runaway and potentially explosive reaction mixtures, and concern for unwanted side reactions that cause lower yields of target aldonic or aldaric acids has created a need for a method for preventing the characteristic rapid and difficult to control reaction temperature rise. Preparation of aldonic and aldaric acids by nitric acid oxidation of carbohydrates and their isolation as their salts (for a review see J. Stanek op. cit.) dates back more than one hundred years. Among the most notable procedures for preparing aldaric acids are nitric acid oxidation procedures for preparing glucaric acid (isolated as the monopotassium salt)(H. Kiliani, Ber., 58, 2344, 1925, 23-25% yield from starch; W. N. Haworth and W. G. M. Jones, J. Chem. Soc., 65, 1944, 45% yield from glucose; C. L. Mehltretter, U.S. Pat. No. 2,436,659, Feb. 24, 1948, 41% from glucose; R. J. Bose, T. L. Hullar, B. A. Lewis and F. Smith, J. Org. Chem., 26, 1300, 1961, 90 g of salt from 200 g of starch). Pilot scale nitric acid oxidation of glucose has been reported to give the same salt in yields of 40-43% (G. C. Mustakus, R. L. Slotter and R. L. Sipf, Ind. Eng. Chem., 46, 427, 1954). Nitric acid oxidation of dextrose has been reviewed (C. L. Mehltretter and C. E. Rist, Agric. and Food Chem., 1, 779, 1953). The monopotassium salt of glucaric acid was also isolated after catalytic oxidation of glucose (C. L. Mehltretter, C. E. Rist and B. H. Alexander, U.S. Pat. No. 2,472,168, Jun. 7, 1949, 54% from glucose).
Free aldaric acids generally have been prepared most conveniently by passing an aqueous solution of a salt over an ion exchange resin or, less so, by metathesis of an insoluble calcium or barium salt with dilute sulfuric acid.
Isolation of a single form of an aldaric acid from the equilibrium mixture of forms (acyclic diacid, multiple acid/lactone, dilactone) which are characteristic of acidic solutions of these acids has been a significant problem associated with preparing aldaric acids by carbohydrate oxidation. Among aldaric acids, galactaric acid is unusual in that it is easy to isolate because a single form dominates the equilibrium mixture and readily crystallizes from aqueous solutions. On the other hand, although glucaric acid forms a somewhat water insoluble monopotassium salt, isolations from glucose oxidations typically are in the 40% range. At the pH where this latter precipitation occurs, the desired monopotassium salt form may be in equilibrium with other salt/acid forms of glucaric acid, which perhaps limits the amount of glucaric acid that is available. Aldonic and aldaric acids tend to form insoluble salts with divalent cations such as calcium and barium but aldaric salts of divalent cations in general have not been isolable as products from nitric acid oxidation of carbohydrates in high enough purity for such a process for their isolation to be practical. For example, calcium glucarate is much more readily prepared from purified monopotassium glucarate than it is directly from a nitric acid oxidation procedure.
Glucaric acid is not presently available on an industrial scale because there is no economic process available (H. Roper, Starch/Starke, 42, 346, 1990). D-glucose (commonly referred to as glucose or dextrose) is a significant commercial product available from starch hydrolysis. Therefore the ability to use glucose as an inexpensive precursor for the corresponding aldaric acid, glucaric acid, in a commercial process would be desirable. A number of uses for glucaric acid have been reported and the commercial availability of comparatively inexpensive glucaric acid could give rise to additional uses. Similarly, other aldonic and aldaric acids which are not presently available commercially might also find applications if the acids could be conveniently prepared from appropriate carbohydrate sources.
Techniques reported to assist in controlling the temperature of a glucose oxidation (60.degree.-64.degree. C.) have included adding a significant amount of sodium nitrite to the reaction (CIBA Ltd., Belgian Patent 615,023, Sep. 13, 1962, yield of monopotassium salt was 46.0-48.5%) or adding the glucose to concentrated nitric acid over a period of time (C. L. Mehltretter, Methods Carbohydr. Chem., 2, 46 (1963); yield of the monopotassium salt was 41%).
Recovery of glucaric acid in forms other than as the monopotassium salt were described even early in this century (see Beilstein's Handbuch der Organischen Chemie, Vierte Auflage, covering the literature until Jan. 1, 1910). More recently glucaric acid lactone salts have been reported (alkali, alkaline earth or ammonium salts of D-glucaric acid 1,4-lactone, E. F. J. Thorpe, German Patent 1,081,443, May 12, 1960). The monopotassium salt form of glucaric acid was also isolated after catalytic oxidation of glucose (C. L. Mehltretter, C. E. Rist and B. H. Alexander, U.S. Pat. No. 2,472,168, Jun. 7, 1949; 54% from glucose). Also difficulties often have been encountered in converting various salts to other salts. Therefore there has been a need for a method for the facile recovery of aldonic and aldaric acid salts.